Effect of parasitism by the pyramidellid gastropod Boonea impressa on the net productivity of oysters (Crassostrea virginica)

The effect of an ectoparasitic gastropod, Boonea (= Odostomia) impressa , on the energy bidget of its host, the American oyster, Crassostrea virginica , was examined. A model was developed from laboratory and field data, as well as from equations developed by Powell and Stanton (1985) . The model predicted that net productivity by large (7 cm length) oysters parasitized by 10 and 30 large (6 mm length) snails would be reduced by 21% and 63%, respectively. In contrast, net productivity in small (3 cm length) oysters would be reduced 25% by only 3 snails. Small oysters would have a negative energy balance when parasitized by 10 snails. The predicted reduction in growth was compared with measured growth in small and large oysters parasitized at abundances typical of Texas oyster reefs. Control oysters (no parasites) gained more shell weight than parasitized oysters. In four-week experiments conducted during the spring and fall, small control oysters gained 86% and 75% more weight than highly parasitized oysters. Large control oysters had 29% and 88% more shell deposition. Snail parasitism produced 75% mortality in small, highly parasitized oysters in the summer. In typical field populations in Texas bays, a minimal estimate of 4–12% of the energy otherwise available to the oyster for growth and reproduction is consumed by Boonea impressa .